Absorbent articles are widely used by both infants and adults in order to receive and contain body exudates. Their wide spread use has spurred significant advances in the materials used to create the absorbent articles as well as the high speed processes by which these materials are created and assembled.
An example of such a material advancement is a stretchable deformable elastic laminate. Typically, elastic laminates comprise a non-elastic substrate bonded to an elastic member. The elastic laminates can be used in a wide variety of locations in an absorbent article. For example, the elastic laminates may be found in a side waist, a back waist, front waist, or crotch region.
One method of producing an elastic laminate involves providing “zero strain” stretch laminate webs which comprise at least two plies of material secured to one another along at least a portion of their coextensive surfaces while in a substantially untensioned (“zero strain”) condition. At least one of the plies employed in the “zero strain” stretch laminate is comprised of a material which is stretchable and elastomeric, i.e., it will return substantially to its untensioned dimensions after an applied tensile force has been released. The second ply secured to the elastomeric ply is elongatable but not necessarily elastomeric. If the second ply is elongatable but not elastomeric, upon stretching, the second ply will permanently elongate at least to a certain degree, so that upon release of the applied tensile forces, it will not fully return to its original undistorted configuration.
The stretching can be induced by mechanical activation which may include meshing the laminate between corrugated mating rolls. This method is called ring rolling and is often performed at high speeds. As an example, a non-elastic material can be plastically deformed in a ring rolling process, thereby reducing the material thickness and creating thin spots in areas where meshing occurs. The laminate experiencing the ring rolling process can be exposed to very high strain rates.
In general, new materials, in order to be proven acceptable in the ring rolling process, are generally tested in the actual process. However, actual process or line testing can be associated with many problems. Specifically, a minimum length of material is needed to engage the ring rolling process. Subsequently, personnel can evaluate the new material downstream of the ring rolling process by counting pinholes or looking for other defects caused by the ring rolling process. Unfortunately, the incorporation of the new material into the process for testing purposes may cause interruptions to manufacturing lines and may require significant personnel time and cost. Moreover, while laminate structures can be tested in the actual process, it is difficult to isolate the effects of various components of the laminate structure. For example, a laminate structure comprising a first nonwoven layer and a second nonwoven layer adhesively bonded together can be tested in the ring rolling process. However, it may be difficult or impossible to isolate the effect of the adhesive on a nonwoven by running the laminate structure through the ring rolling process.
Alternatively, there are some conventional methods of testing new materials. Specifically, new materials can be tested on a tensile tester. While the tensile tester can provide useful information about the new material, the tensile tester may not be able to achieve the strain rates that the new material would be subjected to during an actual ring rolling process. In general, a material can experience strain rates in excess of 1000 s−1 when subjected to an actual ring rolling process.
Moreover, tensile testers may also be limited by a minimum gage length of a sample. The gage length of a material in a standard ring rolling process may be much smaller than 2.0 mm. On a tensile tester, a test sample with a gage length of less than 2 mm may prove difficult to mount on the tensile tester. In addition, the gage length of the sample may interfere with the actual tensile test in that the tensile tester has a much shorter length in which to get to a desired speed such that a desired strain rate can be achieved.
Consequently, it would be beneficial to provide an apparatus and a method for testing new materials which could eliminate the need to test materials in a ring rolling process. In addition, it would be beneficial to provide an apparatus and a method for testing new materials at strain rates which are similar to those provided by ring rolling processes. Also, it would be beneficial to provide an apparatus and a method, for testing new materials, which are capable of utilizing gauge lengths which are similar to those found in ring rolling processes.